refuses to hire you but comes for looking for you in $19 billion. Ened Rebecca Jarvis with the story. Reporter: Meet America's newest billionaires -- Jan koum and Brian Acton -- two engineers who once applied to work for Facebook and got rejected. So, they went to plan B. Started their own business, put everything on the line and tonight, it's Facebook who's pursuing them, agreeing to buy their company, whatsapp, for a cool $19 billion. The reason Facebook is paying so much for whatsapp is, it's really huge. They see it going to a billion users very quickly. Reporter: What they dreamt up, text across the globe without getting hit with huge phone bills. For Jan koum, it's dream come true. Born and raised in a small village in the Ukraine. At 16, he immigrated here to . He and Brian Acton poured their life savings into whatsapp. But koum was hesitant. Zuckerberg wanted to buy whats' app two years ago. The CEO said no thanks. Reporter: On Valentine's day a change of heart. Koum was ready to sell. He came over for dinner and actually interrupted mark Zuckerberg's Valentine's date. Over chocolate-covered strawberries they got the deal signed. Koum chose the very social services office where he used to wait in line to collect food stamps to sign the lucrative deal. Tonight, he's $6.8 billion richer, still never forgetting where he came from. Up next -- sleepless in America.

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